A gun propellant widely used in the western world, including in the United States, is typically constituted of 91 weight percent of nitrocellulose (12.0% N), 1 weight percent of ethyl centralite, 3 weight percent of butyl stearate, 1 weight percent of basic lead carbonate, 1 weight percent of potassium sulfate and 3 weight percent of total volatiles. The military often refers to the gun propellant as BS-NACO.
BS-NACO has been viewed favorably because it is clean burning and cool without requiring the inclusion of soot-producing coolants. BS-NACO, however, has less than desired insensitive munitions (IM) characteristics, i.e., sensitivity to factors that might cause an accidental detonation of the munitions. For example, BS-NACO has a greater sensitivity to slow cook-off and fragment and bullet impact insensitive munitions testing than is desired. For these reasons, certain charges containing BS-NACO propellant are not IM compliant with current military requirements, and currently require an IM waiver to enable their in-service use. While these waivers are acceptable for the short term, ultimately an IM compliant replacement propellant will be needed, particularly in larger gun systems, such as, the US Navy's 5-inch systems and the new “Advanced Gun System” 155 mm guns.
In the past, to make propellants more insensitive, energetics were replaced with inert fillers. However, the substitution of inert fillers for energetics reduces the system energy and therefore impairs performance.